The DefaultWebInterfaceContext does not normally have a context item for $action, however the web items defined in the profile-tabs.xml files rely on this item being defined.

They arguably need be updated to use the more standard $helper.action since this IS part of the DefaultWebInterfaceContext and matches with the webui definitions in global-user-hover-sections.xml and global-user-sections.xml

eg:

    <web-item key="follow" name="Follow Tab" section="system.profile" weight="30">
		<label key="network.name" />
		<link>/users/viewfollow.action?username=$action.username</link>
	</web-item>

would be better as:

    <web-item key="follow" name="Follow Tab" section="system.profile" weight="30">
		<label key="network.name" />
		<link>/users/viewfollow.action?username=$helper.action.username</link>
	</web-item>

Other links in the profile-tabs.xml also use this non-standard context, IMO they should also be updated.